Catalytic Application of Raney Nickel

Abstract

The versatile use of Nickel and its alloys as a catalyst, mostly for hydrogenating organic compounds, can be seen in the chemical industry. Unlike nickel which exits in nature, the alloys of nickel are chemically produced one of which is nickel aluminide, an intermetallic compound. Raney Ni an alloy of nickel is chemically produced and is very finely divided which allows for high reactivity. It is pyrophoric in air. Because of its finely divided composition it has exceptional catalytic properties.

Introduction

In nature, various forms of catalysts exist, the most common of which are enzymes. The crucial roles catalysts play can be observed in the ecosystem and also in the human body. For chemical purposes, catalysts are widely used in order to help increase the rate of a chemical reaction without the catalyst being used up. With that said, enzymes are capable of catalyzing only one reaction. Unlike enzymes, which are known as naturally occurring catalysts, laboratory and industrially prepared catalysts are made in such a way as to mimic the roles or functions of natural catalysts. One of the many types of industrial catalyst is the nickel aluminide commonly known as Raney Nickel which is currently the most active nickel catalyst. [1] The nickel aluminide is a metal catalyst which is composed mostly of nickel and some aluminum and has its formula as NiAl although it is sometimes written as Ni3Al or NiAl3. These three materials are commonly referred to as nickel aluminide or Raney Nickel. The chemical reaction which occurs between a catalyst and the reactant form chemical intermediates which possess different compositions. [2]

Unlike nickel, the nickel aluminum alloys possess high catalytic properties since they are finely grounded and have a higher surface area.

Fig. 8. Apparatus for washing catalyst. It is convenient to have the inlet tube for wash water sealed into the bottom of the chamber rather than introduced through the stopper as shown.

Figure 1: set up for washing catalysts

Preparations

Since nickel is considered a carcinogen, strict safety measures are followed in the preparation of nickel alloys. The synthesis of Raney nickel can be done by first preparing the nickel alloy which is made up of NiAl3 and Ni2Al3. The formed intermetallic compound is then leached in order to obtain NiAl. A traditional method of synthesizing nickel alloys involves mechanical alloying which is done by the melting of nickel in molten aluminum. …need to read more on the preparation. I find it a little confusing.

Structure

Due to the B2 crystal structure, nickel aluminide is considered very strong. The cubic crystal system with ordered structure gives the alloy its strength and hardness making it useful in many industrial processes.

Sponge-like structure

http://ej.iop.org/images/0953-8984/12/34/102/Full/img2.gif

Figure 2: Ni-Al bcc crystal structure

Characterization

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Figure 3: Ni-Al peaks and absorbance

Properties

Raney nickel ignites spontaneously in the presence of air making it pyrophoric when exposed to air. Resistant to high temperatures. During storage, Hydrogen gas escapes making it highly susceptible to fire and explosion hazards. Raney nickel also reacts violently with acids forming H2. They are strong Reducing Agents

http://upload.wikimedia.org/wikipedia/commons/f/f9/Raney_nickel_phase_diagram.png

Fig. 4: Ni-Al phase diagram

Applications

Household uses

Coinage

Transportation

Construction

Petroleum industry

Conclusion

Metals, such as METAL CATALYST, are reducing agents and tend to react with oxidizing agents. Their reactivity is strongly influenced by their state of subdivision: in bulk they often resist chemical combination; in powdered form they may react very rapidly. Thus, as a bulk metal it is somewhat unreactive, but finely divided material may be pyrophoric. The metal reacts exothermically with compounds having active hydrogen atoms (such as acids and water) to form flammable hydrogen gas and caustic products. The reactions are less vigorous than the similar reactions of alkali metals, but the released heat can still ignite the released hydrogen. Materials in this group may react with azo/diazo compounds to form explosive products. These metals and the products of their corrosion by air and water can catalyze polymerization reactions in several classes of organic compounds; these polymerizations sometimes proceed rapidly or even explosively. Some metals in this group form explosive products with halogenated hydrocarbons. Can react explosively with oxidizing materials.

References

1. The Preparation of Raney Nickel Catalysts and their Use Under Conditions Comparable with Those for Platinum and Palladium Catalysts. Homer Adkins, Harry R. Billica. Journal of American Chemical Society, 1948, 70 (2), pp 695–698. Publication Date: February 1, 1948 (Article) DOI: 10.1021/ja01182a080.

2. Bakker, M. L.; Young, D. J.; Wainwright, M. S. (1988). “Selective leaching of NiAl3 and Ni2Al3 intermetallics to form Raney nickels”. Journal of Materials Science 23 (11): 3921–3926.

3. The Role of Hydrogen in Raney Nickel Catalyst. Hilton A. Smith, Andrew J. Chadwell Jr., and S. S. Kirslis. The Journal of Physical Chemistry 1955 59 (9), 820-822

4. Nickel and High-Nickel Alloys. A. J. Marron Ind. Eng. Chem., 1959, 51 (9), pp 1197–1203. Publication Date: September 1959 (Article)

5. Preparation of a Raney Nickel Catalyst. A. A. Pavlic and Homer Adkins. Journal of the American Chemical Society 1946 68 (8), 1471-1471